Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets:
Fixed-maturity securities	$ 11,183	$ 10,823
Other invested assets	88	162
Credit derivative assets	6	13
Liabilities:
Credit derivative liabilities	367	402
Investment funds, fair value	49	48
Recurring [Member]
Assets:
Other invested assets	8	8
Credit derivative assets	6	13
FG VIEs’ assets, at fair value	757	876
Other assets	118	114
Total assets carried at fair value	12,072	11,834
Liabilities:
Credit derivative liabilities	367	402
FG VIEs’ liabilities with recourse, at fair value	689	807
FG VIEs’ liabilities without recourse, at fair value	131	151
Total liabilities carried at fair value	1,187	1,360
Recurring [Member] \| Level 1 [Member]
Assets:
Other invested assets	0	0
Credit derivative assets	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	22	24
Total assets carried at fair value	437	343
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] \| Level 2 [Member]
Assets:
Other invested assets	0	0
Credit derivative assets	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	34	28
Total assets carried at fair value	9,635	9,263
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] \| Level 3 [Member]
Assets:
Other invested assets	8	8
Credit derivative assets	6	13
FG VIEs’ assets, at fair value	757	876
Other assets	62	62
Total assets carried at fair value	2,000	2,228
Liabilities:
Credit derivative liabilities	367	402
FG VIEs’ liabilities with recourse, at fair value	689	807
FG VIEs’ liabilities without recourse, at fair value	131	151
Total liabilities carried at fair value	1,187	1,360
Fixed Maturities [Member]
Assets:
Fixed-maturity securities	10,505	10,233
Fixed Maturities [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,709	5,432
Fixed Maturities [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	289	440
Fixed Maturities [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	2,041	1,613
Fixed Maturities [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	894	987
Fixed Maturities [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	567	583
Fixed Maturities [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	722	945
Fixed Maturities [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	283	233
Fixed Maturities [Member] \| Recurring [Member]
Assets:
Fixed-maturity securities	10,505	10,233
Fixed Maturities [Member] \| Recurring [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,709	5,432
Fixed Maturities [Member] \| Recurring [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	289	440
Fixed Maturities [Member] \| Recurring [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	2,041	1,613
Fixed Maturities [Member] \| Recurring [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	894	987
Fixed Maturities [Member] \| Recurring [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	567	583
Fixed Maturities [Member] \| Recurring [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	722	945
Fixed Maturities [Member] \| Recurring [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	283	233
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member]
Assets:
Fixed-maturity securities	9,338	8,964
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,618	5,393
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	289	440
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	1,978	1,553
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	537	622
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	567	583
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	66	140
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	283	233
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member]
Assets:
Fixed-maturity securities	1,167	1,269
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	91	39
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	63	60
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	357	365
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	656	805
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	0	0
Short-term Investments [Member]
Assets:
Fixed-maturity securities	678	590
Short-term Investments [Member] \| Recurring [Member]
Assets:
Fixed-maturity securities	678	590
Short-term Investments [Member] \| Recurring [Member] \| Level 1 [Member]
Assets:
Fixed-maturity securities	415	319
Short-term Investments [Member] \| Recurring [Member] \| Level 2 [Member]
Assets:
Fixed-maturity securities	263	271
Short-term Investments [Member] \| Recurring [Member] \| Level 3 [Member]
Assets:
Fixed-maturity securities	$ 0	$ 0

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